Mechanical seals comprising a rotatable sealing member and a non-rotatable sealing member having contacting sealing faces are well known in the art. Usually, one of the sealing faces is on the non-rotatable sealing member which is capable of little or no axial movement. The other sealing member is rotatable and axially movable with respect to the non-rotatable member. The rotatable sealing member is urged by resilient means and by fluid pressure, usually of the sealed fluid, toward the non-rotatable sealing member to maintain the sealing faces of the two members in sliding sealing engagement.
Where the fluid pressure applied to the back of the rotatable sealing member to urge the latter toward the non-rotatable sealing member is at least partially counteracted by application of said pressure at the front end of the rotatable sealing member tending to urge the rotatable sealing member away from the non-rotatable sealing member, the seal has become known as a balanced seal. In such a balanced seal, the effective area, i.e., the area on which the sealed fluid (which hereinafter may be referred to as stuffing box fluid) acts on the two sealing faces to urge them together, is always smaller than the bearing area, i.e., the contact area between the rotating and stationary or non-rotating sealing faces. Thus, there is a reduced unit load at the sealing faces in a balanced seal.